Fluoropolymers have properties such as extremely low coefficient of friction, wear and chemical resistance, dielectric strength, temperature resistance and various combinations of these properties that make fluoropolymers useful in numerous and diverse industries. For example, in the chemical process industry, fluoropolymers are used for lining vessels and piping. The biomedical industry has found fluoropolymers to be biocompatible and so have used them in the human body in the form of both implantable parts and devices with which to perform diagnostic and therapeutic procedures. In other applications, fluoropolymers have replaced asbestos and other high temperature materials. Wire jacketing is one such example. Automotive and aircraft bearings, seals, push-pull cables, belts and fuel lines, among other components, are now commonly made with a virgin or filled fluoropolymer component.
Fluoropolymer fibers can be manufactured using one of several processes including dispersion spinning, paste extrusion and melt spinning. For example, dispersion spun or wet fluoropolymer yarns are typically produced by forming a spin mix containing an aqueous dispersion of a non-melt processible fluoropolymer particles and a solution of a cellulosic ether matrix polymer. The spin mix is then extruded at relatively low pressure (e.g., less than 150 pounds per square inch) through an orifice into a coagulation solution usually containing sulfuric acid to coagulate the matrix polymer and form an intermediate fiber structure. The intermediate fiber structure, once washed free of acid and salts, is passed over a series of heated rolls to dry the fiber structure and sinter the fluoropolymer particles into a continuous fluoropolymer filament yarn. Sintering the intermediate fluoropolymer fiber structure causes the fluoropolymer particles in the structure to coalesce and entangle thus forming a continuous fluoropolymer filament fiber.
Paste extruded fibers are typically produced by forming a paste extrusion composition by mixing a non-melt processible or melt processible fluoropolymer fine powder with an organic lubricant. The fluoropolymer soaks up the lubricant, resulting in a dry, pressure coalescing mixture, which is the paste extrusion composition, or simply, the lubricated fluoropolymer powder. The lubricated fluoropolymer powder is placed in an extrusion barrel which terminates in an extrusion head which defines an extrusion orifice. The powder is then “paste extruded” by a ram positioned at the opposite end of the extrusion barrel moving towards the extrusion orifice to force the lubricated fluoropolymer powder through the orifice in such form as sheet, rod, tubing, or coating and through the center of the orifice. The paste extrusion has usually been carried out at a temperature of 20 to 40° C. In most cases, the paste extrudate is then heated to volatilize the lubricant, usually to a temperature of 100 to 250° C., to drive off the lubricant from the extrudate, followed by sintering of the fluoropolymer.
Melt spun fluoropolymer fibers are typically produced by forming granules or pellets of a melt processible fluoropolymer and pumping the melt through a spinneret or die with one to several thousand holes. The molten fibers which exit the spinneret are cooled, solidified and collected on a take-up wheel. Stretching of the fibers in both the molten and solid states provides for orientation of the polymer chains along the fiber axis.